1. Field of the Invention
This invention relates to a surge suppressor and, more particularly, to a modular surge suppressor for an electrical switching device such as a motor starter.
2. Background Information
Electrical switching devices include, for example, circuit switching devices and circuit interrupters such as circuit breakers, contactors, motor starters and motor controllers. Circuit breakers, which are well-known in the art, are generally used to protect electrical circuitry from damage due to an overcurrent condition, such as an overload fault or a relatively high level short circuit condition. Molded case circuit breakers, for example, include at least one pair of separable contacts which are operated either manually by way of a handle disposed on the outside of the case or automatically by way of an internal trip unit in response to an overcurrent condition.
When the circuit breaker is on, a movable contact assembly is in contact with a stationary or fixed contact assembly. The closed contacts conduct a flow of current between a line terminal and a load terminal. When the circuit breaker trips or is switched off, the movable contact assembly is moved away from the fixed contact assembly, thus, interrupting the flow of current between the line and load terminals. Examples of molded case circuit breakers are disclosed in U.S. Pat. Nos. 4,827,369; and 4,963,846.
Additional types of circuit interrupters include, for example, contactors, motor starters, motor controllers, lighting controllers, other load controllers and other electromechanical switching devices used for controlling a variety of electrical loads. Electromagnetic contactors, for example, include a plurality of movable electrical contacts which are brought into contact with a plurality of fixed electrical contacts to close the contactor whenever the coil is energized. On the other hand, whenever the coil is de-energized, the movable electrical contacts are separated from the fixed contacts to open the contactor. Examples of contactors are disclosed in U.S. Pat. Nos. 4,760,364; and 4,766,273.
A common type of starter for loads such as motors, lighting, and the like, comprises an electromagnetic contactor with an overload relay. In a motor starter, for example, the purpose of the overload relay is to estimate the heat produced in the motor by line current and "trip" or stop the motor if the retained heat exceeds an acceptable level. The overload relay monitors the load current and trips the contactor open if a persistent overcurrent condition exists. Typically, the overload relay tracks an I.sup.2 t characteristic of the load current which is a measure of heating.
Today, it is common for the overload relay to contain a microprocessor which digitally generates the I.sup.2 t characteristic. When the calculated I.sup.2 t value reaches a trip level, the contactor is tripped open to interrupt the flow of current to the load.
It is known that switching the coil of a contactor may cause transients. A common solution to this problem is to provide a surge suppressor having wires for attachment of a surge suppression circuit across the contactor coil. However, a user must utilize a screw driver in order to connect or disconnect the surge suppressor to or from the contactor and, hence, there is room for improvement.